Conventionally used is an automatic lighting control device for switching the lamp on when daylight darkens and switching the lamp off when daylight comes back bright by means of furnishing a lamp such as a fluorescent lamp with a photoelectric transducer for detecting daylight brightness.
Consider the case where an automatic lighting control device and a lamp are installed so that the detection field of the photoelectric transducer in the automatic lighting control device overlaps the lamp illumination field entirely or partially. The lamp is switched on when daylight darkens. Then, the light of the switched-on lamp also enters into the photoelectric transducer. The total intensity of the incident light increases. Therefore, the lamp is switched off. This turn-off causes weakening of brightness and the lamp is switched on again. Thus, blink operation is repeated.
Therefore, in the following patent document 1, there is proposed an equipment with an automatic lighting control device installed inside or near the lamp. It switches the lamp on when daylight darkens and it switches the lamp off with a timer when given time passed.
Also, in the following patent document 2, there is already proposed to equip a hood for preventing the incident light to the photoelectric transducer from a lamp. And also, in the following patent document 3, there is already proposed to equip a means for adjusting the detection field of the photoelectric transducer for detecting the brightness.
In the following patent document 4, there is already proposed an automatic lighting control device constituted as follows. Installing a Schmidt trigger circuit able to set up the brightness levels corresponding to light-up and light-out, the lamp is switched on when the output level of the photoelectric transducer for detecting the brightness becomes below the preset light-up level. The lamp is switched off when the output level of the photoelectric transducer rises over the preset light-out level. The difference between the light-up level and the light-out level, i.e., the hysteresis value, is set up greatly. The lamp is made to switch on when the output level falls lower than the light-up level. Thus the lamp is not switched out even if the lamp brightness is superposed.